A high-sensitivity terahertz sensor based on PT phase transition

Abstract

The application provides a high-sensitivity terahertz sensor based on PT phase transition, adopts a PT phase superstructure surface, the PT phase superstructure surface is a periodic structure composed of PT symmetric superstructure units, wherein the superstructure unit is composed of a dielectric substrate, two annular open resonant rings and a tunable material; the two planes where the two annular open resonant rings are located are perpendicular to each other, one annular open resonant ring is located at the center of the surface of the dielectric substrate, and the other annular open resonant ring is located inside the dielectric substrate; the tunable material is located at the notch of the outer annular open resonant ring, and the phase curve of the cross-polarization of the PT phase superstructure surface presents a significant jump at the EP point caused by external excitation change, and the high-sensitivity sensing of the external excitation is realized by using the nonlinear phase jump; compared with the 2D structure, the application effectively avoids the anti-Hermite coupling, reduces the absorption of the system to the electromagnetic wave, and improves the accuracy and efficiency of the sensing.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic waves. In the terahertz frequency band, external excitation changes cause metamaterials to undergo a PT phase transition to achieve high-sensitivity sensing. Specifically, it relates to a high-sensitivity terahertz sensor based on the PT phase transition. Background Technology

[0002] A biosensor is a sensor that detects changes in one or more physical or chemical properties produced when a biosensitive material binds to bioactive substances, including enzymes, nucleic acids, and cell tissues. Single biomolecules mainly include proteins, viruses, and small biological molecules. High-sensitivity detection can quantify individual biomolecules, which plays a crucial role in clinical diagnosis and the detection of potential diseases. Currently, commonly used methods for biomolecule detection include fluorescent labeling, surface plasmon resonance (SPR), and acoustic sensing. However, these methods suffer from drawbacks such as the inability to perform continuous measurements, high cost, long processing times, and limited accuracy, thus reducing detection efficiency and precision.

[0003] Since Bender and Boettcher proved in 1998 that the Hamiltonian of a non-Hermitian system with PT symmetry can also possess real eigenvalues, there has been a great deal of interest in non-Hermitian physics. Much of this research focuses on the Epsilon point (EP point), where the eigenvalues ​​and eigenvectors of PT-symmetric systems are degenerate, the opposite of the phenomenon observed in Hermitian systems. Simultaneously, the transition from the PT-symmetric phase to the PT-broken phase can be studied near the EP point. Metasurfaces are periodic composite structures with subwavelength dimensions. By designing their structures, the distribution of the equivalent permittivity and permeability of metasurfaces can be altered, allowing for the manipulation of parameters such as the amplitude, phase, and polarization state of electromagnetic waves. Non-Hermitian systems have facilitated the design of metasurfaces, enriching the concept. PT-symmetric metasurfaces can realize various important applications, including coherent complete absorption, phase modulation, and polarization manipulation. Research shows that in a system with two coupled structures, the degree of splitting of characteristic frequencies is determined by the square root of the perturbation intensity. Furthermore, in a system with n EP points, the characteristic frequency splitting is typically proportional to the nth root of the perturbation intensity, making the entire system extremely sensitive to sufficiently small perturbations, even capable of sensing changes at the single-molecule level. This novel ultra-sensitive sensing scheme has proven to be a potential method for detecting minute changes in external stimuli, showing great promise for label-free detection of biomolecules, viruses, and proteins. Summary of the Invention

[0004] Purpose of the invention: In order to achieve the high sensitivity detection requirements at the biomolecular level mentioned above, this invention provides a high sensitivity terahertz sensor based on PT phase transition, which is in contrast to existing technologies.

[0005] Technical solution: In order to achieve the above-mentioned high-sensitivity sensing objective, this invention selects the terahertz frequency band and uses two ring open resonators and dielectric materials to form a non-Hermitian system with the external environment. By utilizing the phenomenon that perturbations at the EP point affect the degree of splitting of the system's characteristic frequency, the metasurface can achieve high-sensitivity sensing of external perturbations. Specifically, the external perturbations cause a significant jump in the PT phase.

[0006] A high-sensitivity terahertz sensor based on PT phase transition employs a PT phase metasurface. The PT phase metasurface is a periodic structure composed of PT-symmetric metaunits, where each metaunit consists of a dielectric substrate, two annular open-ring resonators, and a tunable material. The two planes containing the two annular open-ring resonators are perpendicular to each other. One annular open-ring resonator is located at the center of the dielectric substrate surface, and the other annular open-ring resonator is located inside the dielectric substrate. The tunable material is located at the notch of the outer annular open-ring resonator. Changes in external excitation cause a significant jump in the phase curve of the cross-polarization of the PT phase metasurface at the EP point. This nonlinear phase jump is used to achieve high-sensitivity sensing of external excitations.

[0007] 1. The two open-ring resonators are coupled to each other. The dielectric substrate supports the open-ring resonators, and the tunable material is used to sense changes in external excitation.

[0008] 2. The dielectric substrate is a cuboid, and the material is BCB, COC, Polymide, Si, or SiO2.

[0009] 3. The ring-shaped open resonant ring is rhomboid, circular, or square.

[0010] 4. The tunable material is VO2, graphene, or GST.

[0011] Compared with the prior art, the beneficial effects of the present invention are:

[0012] The high-sensitivity terahertz three-dimensional metamaterial sensor based on PT phase designed in this invention utilizes a metamaterial surface to achieve high-sensitivity temperature sensing. It uses the phase change of transmitted electromagnetic waves to characterize temperature changes in the system. Compared to similar terahertz sensors based on electromagnetic wave amplitude sensing, this invention exhibits higher sensitivity. Furthermore, in this invention, the two planes containing the two resonant rings of the metamaterial unit are perpendicular to each other. Compared to 2D structures, this effectively avoids anti-Hermitian coupling, reduces the absorption of electromagnetic waves by the system, and improves the accuracy and efficiency of sensing. Attached Figure Description

[0013] Figure 1This is a three-dimensional structural diagram of a PT-phase meta-unit structure; 1 is the dielectric material, 2 is the first ring open-circuit resonator, 3 is the second ring open-circuit resonator, and 4 is the tunable material;

[0014] Figure 2 This is a schematic diagram showing the change in conductivity of the tunable material VO2 with temperature.

[0015] Figure 3(a) is a transmission curve of circularly polarized electromagnetic waves incident on the PT phase metasurface;

[0016] Figure 3(b) shows the phase distribution of the transmission curve tlr under different VO2 conductivity.

[0017] Figure 3(c) shows the phase change rate of the PT phase metasurface at different temperatures. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] This invention designs a high-sensitivity terahertz sensor based on the PT phase transition, achieving high-sensitivity sensing near the EP point. Combined with... Figure 1 The PT phase metacell consists of a dielectric substrate, a ring-shaped open-circuit resonator, and a tunable material. The dielectric substrate is a cuboid with side lengths Px = Py = 140 μm and a thickness t = 75 μm along the z-axis. Two square open-circuit resonators, 1 and 2, are placed on the surface and inside the dielectric substrate, respectively. Both resonators have a width w = 10 μm and a thickness h = 0.25 μm. Resonator 1 is located inside the dielectric substrate, with a side length l1 = 44.4 μm, an opening width g1 = 6 μm, a distance m = 5 μm from the back surface, and a distance k = 13 μm from the top surface. Resonator 2 is located at the center of the dielectric substrate surface, with a side length l2 = 50 μm and an opening width g2 = 5 μm. A tunable material VO2 with the same thickness as the resonator ring is added at the opening of resonator 2. The open-circuit resonator is made of silver with a conductivity σ = 7 × 10⁶ S / m. The dielectric substrate material is BCB, with a dielectric constant ε = 2.67 and a loss tangent of 0.012. The electromagnetic parameters of VO2 are characterized using the Drude model. ε ∞ =9, ω p =1.40×10¹⁵S⁻¹,ω d =5.75×10¹³S⁻¹, σ₀=3×10⁵S / m, the relationship between the conductivity σ of VO₂ and temperature T is as follows: Figure 2 As shown.

[0020] With the conductivity of VO2 set to σ = 540 S / m, when circularly polarized electromagnetic waves are incident perpendicularly on the metamaterial sensor, an asymmetric transmission phenomenon occurs on the metamaterial surface under the action of the resonant ring, as shown in Figure 3(a), where r and l represent right-handed and left-handed circularly polarized electromagnetic waves, respectively. It can be observed that the two co-polarized transmission curves tll and trr have similar linear shapes and amplitudes, while the cross-polarized transmission curves tlr and trl show significant differences, with the cross-polarized transmission coefficient tlr almost zero at 0.74 THz. By changing the value of the conductivity σ of VO2, the phase distribution of cross-polarization from left-handed to right-handed circular polarization was studied. As shown in Figure 3(b), the phase curve shows a significant phase jump near the EP point, proving that the designed metamaterial surface is sensitive to external temperature changes. Furthermore, the phase curve was differentiated at 0.74 THz, Δφ = |dφ / df|. As shown in Figure 3(b), slight external temperature disturbances cause a significant change in the phase change rate Δφ, and this nonlinear change is crucial for highly sensitive temperature sensing.

[0021] Ultimately, this invention constructs a PT-phase metasurface by placing silver open-cell resonant rings of different sizes on two mutually perpendicular spatial planes based on a BCB dielectric. By adding VO2, the entire metasurface achieves highly sensitive temperature sensing. Subsequently, depending on actual needs, sensing of different frequencies and external excitation variables can be achieved by changing the size of the metasurface units or the type of tunable material.

[0022] The dielectric substrate of this invention exhibits low loss in the corresponding electromagnetic wave frequency band, ensuring high transmittance of electromagnetic waves in the material. The annular open-ring resonator effectively avoids anti-Hermitian coupling, reducing the system's absorption of electromagnetic waves. The annular open-ring resonator should have different geometric dimensions or different materials to ensure different losses between the two resonator rings. The designed PT-phase metasurface and the external environment constitute a passive non-Hermitian system. The metasurface structure is chiral, composed of mutually perpendicular metal resonator rings; the metal material can be one or more of gold, silver, lead, and titanium. The transmission spectrum formed after circularly polarized electromagnetic waves are incident on the PT-phase metasurface is mostly co-polarized transmission, with a small portion being cross-polarized transmission. Different cross-polarized transmission lines exhibit significant asymmetry at the EP point, and one curve is close to 0 at this point. In the metasurface, a tunable material is placed in the gap between the open rings on the surface. Changes in external excitations such as light intensity, temperature, pressure, and voltage alter the conductivity, dielectric constant, and loss parameters of the tunable material. With a fixed structure and material, the loss difference between the two resonator rings can be tuned by changing the external excitation. Depending on actual needs, high-sensitivity sensing of different types of external stimuli can be achieved in microwave, terahertz, or even optical frequency bands by changing the size of the PT phase metacell or the type of tunable material.

[0023] The PT phase metacell of this invention consists of a dielectric substrate, two open-ring resonators, and a tunable material. The two open-ring resonators are coupled to each other. The dielectric substrate supports the open-ring resonators, and the tunable material senses changes in external excitation. The dielectric substrate is cuboid and made of BCB (benzocyclobutene). The two open-ring resonators are square rings, one located on the surface of the dielectric substrate and the other inside. The two planes containing the two open rings are perpendicular to each other, and the resonators are made of metallic silver. The tunable material, VO2 (vanadium dioxide), is located at the notch of the surface resonator and is used for temperature sensing. Different tunable materials can be selected for different changing parameters.

[0024] This invention designs a high-sensitivity terahertz sensor based on the PT (Parity-time Symmetry) phase transition, achieving high-sensitivity sensing near the EP (Exceptional Point). The PT phase metaunit is a single-layer structure composed of a dielectric substrate, two annular open resonant rings, and a tunable material. The two planes containing the two annular open resonant rings are perpendicular to each other, with one open ring located on the surface of the dielectric substrate and the other inside. The tunable material is located at the notch of the surface open ring. When a circularly polarized electromagnetic wave is incident perpendicularly on the metaunit surface, the designed structure exhibits an asymmetric transmission phenomenon, with a significant abrupt change in the phase curve near the EP point, displaying a nonlinear change. This nonlinear change is crucial for sensing external perturbations. In practical applications, sensing of different frequencies and environmental variables can be achieved by changing the size of the metaunit or the type of tunable material. This sensing scheme has great application potential in the field of high-sensitivity virus, protein, and biomolecule detection.

Claims

1. A high-sensitivity terahertz sensor based on PT phase transition, characterized by: A PT phase superstructure is adopted, the PT phase superstructure is a periodic structure composed of PT symmetric super unit, wherein the super unit is composed of a dielectric substrate, two ring-shaped open resonant rings and a tunable material; the two ring-shaped open resonant rings are coupled with each other, the dielectric substrate supports the open resonant ring, and the tunable material is used for sensing external excitation change; the ring-shaped open resonant ring is square; The two planes where the two ring-shaped open resonant rings are located are perpendicular to each other, one of the ring-shaped open resonant rings is located at the center of the surface of the dielectric substrate, and the other ring-shaped open resonant ring is located inside the dielectric substrate; the tunable material is located at the notch of the external ring-shaped open resonant ring, and the external excitation change causes the phase curve of the cross-polarization PT phase superstructure to present a significant jump at the EP point, and the nonlinear phase jump is used to realize high-sensitivity temperature sensing of the external excitation.

2. The high-sensitivity terahertz sensor based on PT phase transition according to claim 1, characterized in that: The dielectric substrate is a cuboid, and the material is BCB, COC, Polymide, Si or SiO2.

3. The high-sensitivity terahertz sensor based on PT phase transition according to claim 1, characterized in that: The tunable material is VO2.

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